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It is any intersection of the axis with a lens surface where the axis is normal (perpendicular) to the lens surface.
Vertex
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An object that produces light and is visible in otherwise total darkness.
Luminous object or source
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An object that do not produce light and are visible only when illuminated by a source.
Nonluminous objects
When light strikes a point on a nonluminous object, is is diffusely reflected or scattered in all directions
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A phenomenon where light symmetrically rebounds in a single direction instead of scattering in many directions.
Specular Reflection
Surfaces that reflect specularly are mirrors, not objects.
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A ______________ occupies no volume, and radiates light in all directions.
Point source
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It is an abstract representation of a light path and not the light moving along this path. It is straight and infinite.
Ray
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It is a rotationally symmetric optical system that produces an ideal image of any object.
Ideal lens
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It refers to the object-image relationship.
Conjugate
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It is the ratio of image height to object height.
Transverse Magnification
Images are scale models of the object, and magnification is the scale factor.
Magnification also indicates the image's orientation with respect to the object. A negative magnification indicates an inverted image.
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Anything that light can travel through, such as glass, liquids, air, avacuum, and even some metals.
medium
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The ratio of light's speed in the vacuum to its speed in the medium.
Refractive Index of a Medium
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It is the variation of refractive index with wavelength
Dispersion
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A principle that states that light travels from point A to point B along the path requiring the least of time.
Fermat's Principle
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It is a line perpendicular to a surface at the point where a ray strikes the surface
surface normal
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It is the angle between the surface normal and the incident ray.
Angle of Incidence
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It is the angle between the surface normal and the reflected ray
Angle of Reflection
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A law that states that the incident ray, reflected ray and the surface normal lies in the same plane and, the angles of incidence and reflection are equal.
The Law of Reflection
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The cornea absorbs rays shorter than ______ nm.
295 nm
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The lens absorb light shorter than _____ nm.
350 nm
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It is a phenomenon of change in the path of light rays without any change in the medium.
Reflection of light
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The law of reflection states:
- The incident ray, the reflected ray and the normal at the point of incident, all lie in the same plane
- The angle of incidence is equal to the angle of reflection
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A smooth and well-polished surface which reflects regularly most of the light falling on it is called ________.
Mirrors
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The features of an image formed by a PLANE MIRROR:
- It is of the same size as the object
- It lies at the same distance behind the mirror as the object is in front
- It is laterally inverted
- Virtual in nature
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It is a part of a hollow sphere whose one side is silvered and the other side is polished.
Spherical Mirror
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Cardinal points of a concave mirror
- Principal Focus or Focal Point (F)
- Focal Length (f)
- Center of Curvature (C)
- Radius of Curvature (R)
- Pole of the Mirror (P)
- Principal Axis of the Mirror
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It is the straight line joining the pole and center of the curvature of spherical mirror and extended on both sides.
Principal Axis of the Mirror
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It is a point on the principal axis of the mirror at which, ray incident on the mirror in a direction parallel to the principal axis actually meet (in concave mirror) or appear to diverge (as in convex mirror) after reflection from the mirror.
Principal Focus (F)
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It is the distance of principal focus from the pole of the spherical mirror.
Focal length (f)
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It is the phenomenon of change in the path of light, when it goes from one medium to another. Its basic cause is the change in the velocity of light going from one medium to the other.
Refraction
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Laws of Refraction
- The incident and refracted rays are on opposite sides of the normal and all the three are in the same plane
- The ratio of sine of angle of incidence to the sine of angle of refraction is constant for the part of media in contact.
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A phenomenon when a ray of light travelling from an optically-denser medium to an optically-rarer medium is incident at an angle greater than the critical angle of the pair of media in contact, the ray is totally reflected back into the denser medium
Total Internal Reflection
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It refers to the angle of incidence in the denser medium, corresponding to which angle of refraction in the rare medium is 90'.
Critical Angle
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It is a refracting medium, having two plane surfaces, inclined at an angle.
Prism
The greater the angle formed by two surfaces at the apex, the stronger the prismatic effect.
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It is a transparent refracting medium, bounded by two surfaces which form a part of a sphere or cylinder.
Lens
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This corresponds to the nodal point of a thick lens. It is a point on the principal axis in the lens, the rays passing from where do not underfo deviation.
Optical Center of the lens (O)
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It is defined as the ability of the lens to converge a beam of light falling on the lens.
Power of a lens ( P)
- convex - positive (converging)
- concave - negative (diverging)
measured as reciprocal of the focal length in meters ( P = 1/f)
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Termed as "objective refraction," which is a clinical test used to determine the approximate nature and extent of a patient's refractive error
Retiniscopy
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This test provides a precise measurement of refractive error and appropriate lens correction by utilizing patient's reaction and participation. It is also termed as objective refraction.
Refinement
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The final step in refraction that determines whether accommodation has been equally relaxed in both eyes
Binocular balancing
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The average power of a spherocylindrical lens is called __________.
spherical equivalent
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